Two conductor measuring device, method for testing the same and testing system therefor

ABSTRACT

A two conductor measuring device (MS) is supplied with a current of a current loop, which originates from a source circuit (Q). The source circuit is certified in accordance with a valid standard IEC-1000-4-5, especially in accordance with standard IEC-1000-4-5:1995, is supplied with power by a primary vehicle electrical system (NP), and serves to supply a secondary vehicle electrical system (NS) with power. The two conductor measuring device (MS) is designed in such a way that it cannot be certified for an electromagnetic compatibility in accordance with valid standard IEC-1000-4-5. During testing the two conductor measuring device (MS) for electromagnetic compatibility, a hybrid generator, especially in accordance with standard IEC-60-1 or IEC-469-1, is used for generating a current/voltage surge. A decoupling network for simulating the source circuit (Q) is connected in an outgoing circuit to the hybrid generator. A two conductor measuring device (MS), which does not satisfy the test specifications of the standard IEC-1000-4-5:1995, is connected in the outgoing circuit to the decoupling network, and a type of approval for use on the secondary vehicle electrical system (NS) is granted to other two conductor measuring devices of the same type when the tested two conductor measuring device has withstood the test.

RELATED APPLICATIONS

This application claims the priority of the PCT International PatentApplication No. PCT/EP01/o4386, filed Apr. 18, 2001, which is based onEPO Patent Application No. 00110818.2 filed May 22, 2000.

FIELD OF THE INVENTION

The invention relates to two conductor measuring devices, methods fortesting such devices, and testing systems designed for use in performingthe tests.

BACKGROUND OF THE INVENTION

In the following discussion, reference is made to FIG. 1. As is known,two conductor measuring devices are measuring devices that are equippedwith only two conductors L1, L2, which enable them to be electricallyconnected from and to the outside. These two conductors must be usedboth for supplying energy and for transmitting a measuring signalgenerated by the measuring device. The measuring signal values producedby the two conductor measuring device are direct currents within astandardized range of 4 mA to 20 mA, such that one current value withinthis range corresponds precisely to one measuring signal value.

The above-mentioned supplying of energy is accomplished by means of adirect current source that, during operation, is connected to the twoconductors from the outside, generates a direct current, and belongs toa primary network NP, so that a so-called current loop is created. Thisloop also contains a current measuring resistor Rm, where a current thatis proportional to the current value at any given time, and thus to themeasuring signal, can be tapped and further processed.

The resistor Rm can be positioned a great distance from the twoconductor measuring device MS, in this case it is connected to themeasuring device via cables of appropriate length. Specifically, theterminal NP1 of the primary network NP is connected to the conductor L1of the two conductor measuring device MS′, and the terminal NP2 isconnected to one port of the resistor Rm, while the resistor's otherport is connected to the conductor L2 as an indirect second primarynetwork port NP2′, as it were.

In addition to the above-mentioned current values, which are analogsignals, digital signals can also be transmitted at the two conductorsL1, L2, in accordance with one of the customary standards, such as theso-called HART protocol. The HART protocol (HART is a registeredtrademark of the HART User Group and is an acronym for “HighwayAddressable Remote Transducer”, in other words for bus-addressedmeasuring devices) has long been known and used in industrial measuringtechnology.

The HART protocol enables communication between a field level and aprocess control level, providing the advantage of simultaneoustransmissibility of an analog measuring signal in accordance with the4-mA to 20 mA standard, and of the digital HART signal for start-up,maintenance, polling, or control of the measuring devices in the fieldlevel.

While the analog measuring signal is continuously available, cyclicalpolling and, if necessary, a subsequent instruction via the digital HARTsignals takes place. In this process, a digital zero is realized via twosine-wave oscillations at a frequency of 2.2 kHz, and a digital one isrealized via a single sine-wave oscillation at a frequency of 1.2 kHz,in keeping with the standard Bell 202 Frequency Shift Keying. Thesesine-wave oscillations are transmitted via the two conductors, in thatthey are modulated upon the current flowing therein.

Current state-of-the-art two conductor measuring devices arecompetitive, in other words marketable by the manufacturer, only if theyhave been tested for electromagnetic compatibility (abbreviated: EMV).The testing must be conducted in compliance with the currently validinternational standard IEC-1000-4-5:1995, which has been adopted inindividual countries to correspond with national standards, and is aso-called type test.

In a type test, each individually produced device is not tested.Instead, the testing of one or a few devices from a group of identicaldevices is sufficient.

The standard IEC-1000-4-5:1995 has been valid since 1995. According tothe previous version, which was valid until 1995, the two conductors L1,L2 were considered only as signal lines used to transmit measuringsignals, and thus were not subject to the more rigorous specificationsfor energy supply lines, for which the conductors were tested.

In 1995, however, this approach and classification was tightened, withthe direct connection of the two conductor measuring devices to thedirect current source G and/or its primary electrical system NP; the twoconductors L1, L2 now are no longer defined merely as signal lines, butalso as supply lines, hence they are subject to the above-named rigidtest specifications and are tested on that basis.

These test specifications require that the primary electrical systemthat serves to supply energy and originates from the direct currentsource Q also generate high-energy interference pulses in addition tothe direct current, which a two conductor measuring device MS′ that isconnected to the network must withstand.

These test specifications simulate real conditions such as occur inpractice when two conductor measuring devices e.g. are to be used formeans of transport, especially in ships. In a primary vehicle electricalsystem NP installed on a ship, the above-mentioned interference pulsesare frequently present, (FIG. 1). Hence, the two conductors L1, L2, instate-of-the-art two conductor measuring devices must be tested usingthe test signals based upon the standard IEC-1000-4-5:1995 for energysupply lines, hence they are to be dimensioned to be resistant relativeto these test signals.

This does not make sense in practical terms, however, since it wouldmean that in the two conductor measuring device MS′, which is equippedwith a standardized case Gh, electronic components, i.e. a conductancecoil L′ and a condenser C′, would have to be incorporated at the inputside in a suitable combination, serving to suppress or at least filterthe interference pulses that occur in the primary vehicle electricalsystem NP.

These incorporated elements, however, increase production costs.Furthermore, the dynamic space SF required for these filter components,which in most cases must be installed in multiples, is not available, sothat the size of the standardized casing Gh must be increased by acasing volume Gz, which increases costs substantially. Finally, theapplicability of the above-mentioned HART protocol is severely curtailedas a result of the filter components, and in some cases is renderedimpossible.

SUMMARY OF THE INVENTION

One object of the invention is to provide a two conductor measuringdevice intended for use in means of transport, especially in a ship Afurther object of the invention is to provide a method for testing theelectromagnetic compatibility of a two conductor measuring device thatis intended for use in a means of transport, especially in a ship, inaccordance with the standard IEC-1000-4-5:1995.

Another object of the invention is to provide a test system for testingthe electromagnetic compatibility of a two conductor measuring devicethat is intended for use in a means of transport, especially in a ship.Finally, an object of the invention consists in providing a method forgranting approval for use of a two conductor measuring device that isintended for use in a means of transport, especially in a ship.

To attain these objects, a first variant of the invention consists of atwo conductor measuring device

-   -   that is intended for use in a means of transport, especially in        a ship,    -   wherein it is supplied on-board with current from a current        loop,    -   which originates from a source circuit that is certified in        accordance with a valid standard IEC-1000-4-5, especially the        standard IEC-1000-4-5:1995, is supplied with power by a primary        vehicle electrical system of the means of transport, and serves        to supply a secondary vehicle electrical system with power, and    -   wherein the two conductor measuring device is designed such that        it cannot be certified for electromagnetic compatibility in        accordance with the valid standard IEC-1000-4-5.

To attain the above-mentioned objects, a second variant of the inventioncomprises a method for testing the electromagnetic compatibility of atwo conductor measuring device that is intended for use in a means oftransport, especially a ship, where it is supplied on-board with currentfrom a current loop, which originates from a source circuit that iscertified in accordance with a valid standard IEC-1000-4-5, especiallythe standard IEC-1000-4-5:1995, is supplied with power by a primaryvehicle electrical system of the means of transport, and serves tosupply a secondary vehicle electrical system with power, in which method

-   -   a hybrid generator, especially one that is in accordance with        the standard IEC-60-1 or IEC 469-1, is used to generate a        current/voltage surge,    -   a decoupling network for simulating 5 the source circuit is        connected in outgoing circuit to the hybrid generator,    -   a two conductor measuring device, which does not satisfy the        test specifications of the standard IEC-1000-4-5:1995, is        connected in outgoing circuit to said decoupling network, and    -   an 10 approval for use in the secondary vehicle electrical        system is granted to other two conductor measuring devices of        the same type when the tested two conductor measuring device has        withstood the test.

To attain the above-named objects, a third variant of the inventioncomprises a test system for testing the electromagnetic compatibility ofa two conductor measuring device that is intended for use in a means oftransport, especially a ship, where it is supplied on-board with currentfrom a current loop, which originates from a source circuit that iscertified in accordance with a valid standard IEC-1000-4-5, especiallythe standard IEC-1000-4-5:1995, is supplied with power by a primaryvehicle electrical system of the means of transport, and serves tosupply a secondary vehicle electrical system with power; wherein thistest system comprises:

-   -   a hybrid generator, especially one in accordance with the        standard IEC-60-1 or IEC 469-1, for generating a current/voltage        surge,    -   a decoupling network for simulating the source circuit,        connected in outgoing circuit to the hybrid generator, and    -   a two conductor measuring device that does not satisfy the test        specifications of the standard IEC-1000-4-5, and is connected in        outgoing circuit to said decoupling network.

To attain the above-mentioned objects, a fourth variant of the inventionconsists in a method for granting an approval for use of a two conductormeasuring device that is intended for use in a means of transport,especially in a ship, where it is supplied on-board with current from acurrent loop, which originates from a source circuit that is certifiedin accordance with a valid standard IEC-1000-4-5, especially thestandard IEC-1000-4-5:1995, is supplied with power by a primary vehicleelectrical system of the means of transport, and serves to supply asecondary vehicle electrical system with power, in which method theapproval for use of the two conductor measuring device is granted onlyif it is to be used exclusively in the certified source circuit of themeans of transport, without being certified in accordance with the testspecifications of the current valid standard IEC-1000-4-5.

One significant advantage of the invention consists in the fact that, intwo conductor measuring devices that are to be used in means oftransport, especially in ships, no costly components that requiredynamic space and suppress and/or filter interference pulses arenecessary, and in that an approval for use according to the standard IEC1000-4-5:1995 can nevertheless be granted for such two conductormeasuring devices.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a known two conductor measuring device (MS) withoutside connections; and

FIG. 2 illustrates a two conductor measuring device (MS) with outsideconnections according to the present invention.

FIG. 3 illustrates a hybrid generator, the decoupling network and themeasuring device in block diagram form.

The invention will be described below in greater detail, with referenceto the second figure in the diagrams, FIG. 2, in which an exemplaryembodiment of a two conductor measuring device is illustratedschematically in the form of a block diagram.

DESCRIPTION OF THE PREFERRED EMBODIMENT

In FIG. 2, a traditional two conductor measuring device MS, e.g. with astandard casing Gh, is depicted as a circuit block. At least onephysical dimension is measured by the two conductor measuring device MS,i.e. the volumetric or mass flow of a fluid, or its density, viscosity,pressure, or temperature, or even the difference in pressure between twomedia, or very generally the temperature, pressure, level, pH value, orgas concentration.

Because the invention relates not to the measuring principle of the twoconductor measuring device MS and its electronic circuitry, specificallyits evaluation electronics, but rather relates to its certificationindependent of the measuring principle, its circuit block is notillustrated or described in any greater detail.

The two conductor measuring device MS is intended for use in a means oftransport, especially a ship. There it is supplied on-board with currentfrom a current loop, which originates from a source circuit Q that iscertified in accordance with a valid standard IEC-1000-4-5, especiallythe standard IEC-1000-4-5:1995, is supplied with power by a primaryvehicle electrical system NP of the means of transport, and serves tosupply a secondary vehicle electrical system NS with power.

The two terminals NP1, NP2 thus lie at supply terminals for the sourcecircuit Q, one active part of which is presented, for the sake ofsimplicity, as the source g of a direct current, with filter components,such as an inductance coil and a condenser C, being presented ascomponents of this active part, so that a secondary vehicle electricalsystem NS with the terminals NS1, NS2′ is created at its output. In thiscase as well, the current measuring resistor Rm is connected between theterminal NS2 and the conductor L2, hence the terminal of the resistor Rmthat faces the measuring device can be referred to as an indirectterminal of the secondary vehicle electrical system NS2′.

The filter components are dimensioned, conceived, and designed such thatthe secondary vehicle electrical system NS complies with a validstandard IEC-1000-4-5, especially the standard IEC-1000-4-5:1995, andthus can be tested and certified in accordance with this standard.

On the basis of this inventive design, the two conductor measuringdevice MS surprisingly needs only to be designed such that it cannot beEMV certified for electromagnetic compatibility in accordance with thevalid standard IEC-1000-4-5.

Hence, an approval for use of a two conductor measuring device MSintended for use in a means of transport, especially in a ship, can begranted as follows, i.e. it can be EMV certified as follows: When in usein the means of transport, the two conductor measuring device MS issupplied on-board with current from a current loop, wherein the currentoriginates from a source circuit Q that is certified in accordance witha valid standard IEC-1000-4-5, especially the standardIEC-1000-4-5:1995, is supplied with power by a primary vehicleelectrical system NP of the means of transport, and serves to supply asecondary vehicle electrical system NS with power. The source circuit isin compliance with the test specifications of the valid standardIEC-1000-4-5 and will be or is already EMV certified, in other words itpossesses this approval for use and/or the corresponding certificate.

Thus the approval for use of the two conductor measuring device, inother words its EMV certificate, is granted in accordance with the validstandard IEC-1000-4-5 only if, without being EMV certified in accordancewith the test specifications of the valid standard IEC-1000-4-5:1995, itwill be used exclusively in the EMV-certified secondary vehicleelectrical system of the means of transport. In order to fulfill thiscondition, the two conductor measuring device MS may be equipped e.g.with a correspondingly dimensioned terminal connecting device.

The method specified in the invention for testing the electromagneticcompatibility of the two conductor measuring device MS that is intendedfor use in a means of transport, especially in a ship, is implemented asfollows (the measuring device MS in this case is also supplied with theabove-described current from the current loop that contains the sourcecircuit Q):

A hybrid generator (10), especially in accordance with the standardIEC-60-1 or 10 IEC 469-1, generates a current/voltage surge, especiallythe current/voltage surge defined in this standard in reference to thetemporal course of the open-circuit voltage and the temporal course ofthe short-circuit current. A decoupling network (12), also defined bythe above-mentioned standard, for simulating the source circuit Q isconnected in outgoing circuit to the hybrid generator, and a twoconductor measuring device MS (14), which does not satisfy the testspecifications of the standard IEC-1000-4-5:1995 is connected inoutgoing circuit to said decoupling network (FIG. 3).

The approval for use in the secondary vehicle electrical system NS ofthe means of transport is granted to other two conductor measuringdevices, hence the EMV certification is granted them, when the testedtwo conductor measuring device MS has withstood the test.

A test system, specified in the invention, for testing theelectromagnetic compatibility of a two conductor measuring device thatis intended for use in a means of transport, especially in a ship,comprises the above-mentioned hybrid generator, especially in accordancewith the standard IEC-60-1 or IEC 469-1, for generating theabove-described current/voltage surge, the decoupling network connectedin outgoing circuit to the hybrid generator and intended for simulatingthe secondary vehicle electrical system NS, and the two conductormeasuring device that is connected in outgoing circuit to the decouplingnetwork and is not certified in accordance with the test specificationsof the valid standard IEC-1000-4-5.

1. A two conductor measuring device (MS) for use in transport,especially in a ship, comprising: a source circuit (Q), certified inaccordance with a valid standard, IEC 1000-4-5; a primary vehicleelectrical system (NP); and a secondary vehicle electrical system (NS),wherein: said source circuit (Q) is supplied with primary power by saidprimary vehicle electrical system (NP); said source circuit (Q) servingto supply power to said secondary vehicle electrical system (NS); thetwo conductor measuring device (MS) is supplied on-board the shiptransport with current from a current loop, the current originating fromsaid source circuit (Q) and the two conductor measuring device generatesa measuring signal value and transmits the measuring signal value viasaid current loop; and the two conductor measuring device (MS) isdesigned such that it cannot be certified for electromagneticcompatibility in accordance with the valid standard, IEC-1000-4-5. 2.The two conductor measuring device (MS) as defined in claim 1, whereinthe valid standard is IEC-1000-4-5:1995.
 3. The two conductor measuringdevice as claimed in claim 1, wherein the two conductor measuring devicemeasures at least one physical dimension being selected from a groupconsisting of a volumetric flow of a fluid, a mass flow of a fluid, adensity of a fluid, a viscosity of a fluid, a pressure of a fluid, atemperature of a medium, difference in pressure between two media, alevel, a pH value and a gas concentration.
 4. A method for testing theelectromagnetic compatibility of a two conductor measuring device (MS)for use in transport, especially in a ship, the two conductor measuringdevice (MS) being supplied on board the transport with current from acurrent loop, which originates from a source circuit that is certifiedin accordance with a valid standard IEC-1000-4-5, with power by aprimary vehicle electrical system (NP) of the transport, and serves tosupply a secondary vehicle electrical system (NS) with power, and thetwo conductor measuring device generates a measuring signal value andtransmits the measuring signal value via said current loop, said methodcomprising the steps of: generating a current/voltage surge with ahybrid generator, especially in accordance with one of: the standardIEC-60-1, and IEC 469-1; connecting a decoupling network in outgoingcircuit to the hybrid generator for simulating the source circuit (Q);connecting in outgoing circuit to the decoupling network of a twoconductor measuring device which does not satisfy the testspecifications of the standard IEC-1000-4-5; and granting approval foruse in the secondary vehicle electrical system (NS) other two conductormeasuring devices of the same type when the tested two conductormeasuring device has withstood the test.
 5. The method as defined inclaim 4, wherein the valid standard is IEC-1000-4-5:1995.
 6. The methodas claimed in claim 4, wherein the two conductor measuring device to betested serves to measure at least one physical dimension being selectedfrom a group consisting of a volumetric flow of a fluid, a mass flow ofa fluid, a density of a fluid, a viscosity of a fluid, a pressure of afluid, a temperature of a medium, difference in pressure between twomedia, a level, a pH value and a gas concentration.
 7. A system fortesting the electromagnetic compatibility of a two conductor measuringdevice (MS) for use in transport, especially in a ship, the twoconductor measuring device (MS) being supplied on board the transportwith current from a current loop, which originates from a source circuit(Q) that is certified in accordance with a valid standard, IEC-1000-4-5,with power by a primary vehicle electrical system (NP) of the transport,and serves to supply a secondary vehicle electrical system (NS) withpower, and the two conductor measuring device generates a measuringsignal value and transmits the measuring signal value via said currentloop, said method comprising: a hybrid generator, especially inaccordance with one of: the standard IEC-60-1, and IEC-469-1, forgenerating a current/voltage surge; a decoupling network connected inoutgoing circuit to said hybrid generator for simulating the sourcecircuit (Q); and a two conductor measuring device (MS) connected inoutgoing circuit to said decoupling network, said two conductormeasuring device (MS) being not certified in accordance with the testspecifications of the valid standard, IEC-1000-4-5.
 8. The system asdefined in claim 7, wherein the valid standard is IEC-1000-4-5:1995. 9.The method as claimed in claim 7, wherein the two conductor measuringdevice to be tested serves to measure at least one physical dimensionbeing selected from a group consisting of a volumetric flow of a fluid,a mass flow of a fluid, a density of a fluid, a viscosity of a fluid, apressure of a fluid, a temperature of a medium, difference in pressurebetween two media, a level, a pH value and a gas concentration.
 10. Amethod for granting approval for a two conductor measuring device (MS)for use in transport, especially in a ship, the two conductor measuringdevice (MS) being supplied on board with current from a current loop,which originates from a source circuit (Q) that is certified inaccordance with a valid standard, IEC-1000-4-5, with power by a primaryvehicle electrical system (NP) of the transport, and serves to supply asecondary vehicle electrical system with power, and the two conductormeasuring device transmits a measuring signal value via said currentloop, said measuring signal value is generated by the two conductormeasuring device, said method comprising the step of: granting approvalfor the use of the two conductor measuring device (MS) only when it isused exclusively in the certified secondary vehicle electrical system(NS) of the transport, without being certified in accordance with thetest specifications of the valid standard, IEC-1000-4-5.
 11. The methodas defined in claim 10, wherein the valid standard is IEC-1000-4-5:1995.12. The method as claimed in claim 10, wherein the two conductormeasuring device to be approved serves to measure at least one physicaldimension being selected from a group consisting of a volumetric flow ofa fluid, a mass flow of a fluid, a density of a fluid, a viscosity of afluid, a pressure of a fluid, a temperature of a medium, difference inpressure between two media, a level, a pH value and a gas concentration.